Packing machines are known which produce packing containers of the non-returnable type by converting a flexible web of packing material to a material tube, successively filling the tube with contents and sealing the same in repeated transverse sealing zones placed at uniform intervals (U.S. Pat. No. 3,325,961). In this type of machine the contents are fed via one or more feed ducts which in the form of a filling pipe extend substantially vertically downwards into the packing material tube and open at some distance from the bottom of the same, that is to say slightly above the place where the repeated transverse sealing of the downwards directed tube occurs. Thus the feed ducts as well as the outside of the filling pipe come into contact with the contents, and it is therefore very important that it should be possible to cleanse and sterilize these parts in an effective manner before the machine is started and production commences (so-called presterilization). At the same time the adjacent, inner part of the packing material tube must be sterile, and if this is the case this sterility must not be allowed to be disrupted. This means in practice that the lower part of the filling pipe surrounded by the packing material tube is not accessible for manual cleaning or sterilization from the outside.
A further difficulty is caused by the fact that the strong cleaning and sterilizing agent which has to be used for removing residues of contents and for sterilizing the internal, inaccessible parts of the feed ducts must not come into contact with the packing material tube consisting of paper or plastics, since this may then be destroyed and commence to leak so that the sterility might be lost. The sterilizing agent, moreover, is delivered to the feed ducts under high pressure which would immediately burst the tube if the sterilizing agent were to be allowed to flow into the same. None the less, the inside of the packing material tube as well as the outside of the filling pipe have to be sterilized prior to the start of production, that is to say before the packing machine is started to produce aseptic packing containers filled with sterile contents.
When a packing machine for example of the type described above is to be presterilized before the start of production, a sterilization process will have to be utilized, therefore, which involves a change from the sterilization of the feed ducts, the outside of the filling pipe and the inside of the packing material tube to a subsequent production situation without any disruption of the sterility achieved. It must be possible to carry out the transition from internal sterilization of the feed ducts to external sterilization of the filling pipe without the occurrence of a risk reinfection of the feed ducts, that is to say without their inside being brought into contact with the environment.
Earlier attempts to provide a cleaning and sterilization process on similar packing machines included dismantling of parts of the filling pipe for manual cleaning and sterilization. It was not possible during the manual mounting of the filling pipe completely to avoid the risk of reinfection.